A stator of rotating machinery, such as an electric power generator, generally includes a stator core and a stator frame. The stator core typically has a cylindrical shape and consists of coaxially stacked insulated ferrous laminations. Conventional laminations are formed from semi-circular lamination sections that when spaced around a common axis form an entire lamination. Each lamination has slots to accommodate a stator winding and cutouts defined on its peripheral edge to define key bar grooves for accommodating key bars.
Key bars are provided along the peripheral edge of the laminations, radially spaced apart along its periphery, to provide structural support. For example, in conventional assemblies, the cutouts formed in the lamination sections can be formed in a dovetail shape to compliment a dovetail shape of the inward facing edge of each key bar. During assembly, each lamination can be installed onto one or more corresponding key bars by sliding onto or over the dovetail. Thus, key bars aid in orienting and assembling the lamination sections when forming a stator core, and also provide structural integrity after assembly and during operation.
In conventional stator assemblies, such as illustrated by the example stator assembly 100 in FIG. 1, multiple core support rings 110 are welded or otherwise affixed to the key bars 120 and integrated with the stator frame within which the stator core is contained. Similarly, multiple rigid core rings 140 are welded to or otherwise affixed to the key bars 120. The core support rings 110 serve to integrate the stator core with the stator frame (e.g., affixed to the stator frame or integrated via spring bars 150). The multiple rigid core rings 140 serve to provide additional structural integrity to the key bars 120 and the stator core, attempting to maintain the key bar 120 positions within a predefined tolerance.
During operation, however, the stator core changes shape due to the electromagnetic force pulling each lamination section inwardly toward the central axis defined through the center of the stator core. For example, in some installations, a stator core can be subject to movements at a frequency at or near 120 Hertz. The rapid stator core movements in turn cause a condition commonly referred to as “key bar rattle,” whereby the lamination sections rattle against the key bars due to the voids that may exist between the key bar dovetails and the lamination cutouts. In an attempt to counter key bar rattle, flat, conventional compression bands 160 have been positioned around the key bars 120 between the rigid core rings 140. The conventional, flat compression bands 160 can be tightened to exert an inward radial force in an attempt to tighten key bars 120 against the laminations within a desired tolerance. However, due to the rigid core rings 140 placed along the length of the stator core and welded to the key bars 120, the conventional, flat compression bands 160 and the rigid core rings 140 oppose each other. For example, the rigid core rings 140 have an inner diameter and retain the key bars 120 to that inner diameter. However, when the conventional, flat compression bands 160 are placed around the key bars 120 and an inward radial force is exerted, the key bars 120 remain attached to the rigid core rings 140 at the inner diameter and resist the inward radial force exerted by the conventional, flat compression bands 160. In these conventional assemblies, the rigid core rings 140 were installed to provide both radial and circumferential integrity to the key bars 120, and thus the stator core laminations. The conventional, flat compression bands 160 were added to reduce key bar rattle.
Accordingly, there exists a need for an apparatus to control key bar movement while providing structural integrity to a stator core assembly.
Furthermore, a need exists for systems, methods, and apparatus for controlling key bar movement in a stator assembly.